The present invention relates to lifters for activating valves in response to rotation of a camshaft in an internal combustion engine; more particularly, to such lifters having means for selectively engaging and disengaging such activation; and most particularly, to a valve lifter wherein operational reliability is substantially increased through improved features of various components and wherein a means for lash adjustment is provided.
It is well known that overall fuel efficiency in a multiple-cylinder internal combustion engine can be increased by selective deactivation of one or more of the engine cylinders by the deactivation of intake and exhaust valves, under certain engine load conditions. A known approach to providing selective valve deactivation in a push rod engine is to equip the lifters for those valves with means whereby the lifters may be rendered incapable of transferring the cyclic motion of engine cams into reciprocal motion of the associated pushrods and valves. Typically, a deactivation lifter in a push rod engine includes concentric inner and outer portions which are mechanically responsive to the pushrod and to the cam lobe, respectively, and which may be selectively latched and unlatched to each other, typically by controlling the position of a locking member within the lifter by the selective application or removal of pressurized engine oil to the locking pins. The lifter may also include a conventional hydraulic lash compensation means as known in the art.
U.S. Pat. No. 6,164,255, issued Dec. 26, 2000 to Maas et al., discloses a deactivation hydraulic valve lifter comprising an outer section which encloses an inner section that is axially movable relative therein, the outer section having a pot-shaped configuration and a bottom which comprises an end for cam contact and separates the inner section from a cam whereby, upon coupling of the sections by a coupling means, a high lift of a gas exchange valve is effected, and upon uncoupling of the sections, a zero lift. The disclosed coupling means is a single round pin disposed in a transverse bore in the inner section and biased outwards by a coil spring to engage a mating bore in the outer section, whereby the two sections may be locked together. The bore in the outer section is matable with an oil gallery in the engine block, whereby pressurized oil may be introduced against the head of the locking pin to urge the pin hydraulically into retraction within the inner section to uncouple the inner and outer sections and thereby deactivate the associated engine valve.
In order for the locking pin to engage reliably into the outer section bore, the bore must be somewhat oversize to accommodate rotational and axial alignment tolerances. However, this can result in high contact stress between the pin and the bore, and also some sliding movement as the pin moves into contact at the lowest point in the bore, both of which can result in undesirably high wear rates leading to noisy actuation and possible failure of the lifter. Further, the asymmetric nature of the load path in a single locking pin design such as that disclosed in Mass et al., can result in operational stiffness of the lifter deactivation mechanism, accelerated wear, and unpredictable leak down of the hydraulic element due to tipping of the inner body from the asymmetric loading.
U.S. Pat. No. 6,321,704 B1, issued Nov. 27, 2001 to Church et al., the relevant disclosure of which is herein incorporated by reference, discloses a mechanism purportedly useful in a valve-deactivating hydraulic lash adjuster or a valve deactivating hydraulic lifter. The mechanism is similar to that disclosed by Maas et al. but includes a pair of opposed locking pins disposed in a transverse bore in the inner section to engage the outer section in two separate locations 180xc2x0 apart. Further, the outer section single bore of Maas et al. is replaced by an annular groove formed in the inner wall of the outer section and defining an annular locking surface such that all rotational alignment requirements are removed, the pins being engageable into the groove at all rotational positions of the inner section within the outer section. The groove communicates, similarly to the bore in Maas et al., with an oil gallery in the engine block for actuation and deactivation of the locking pins. Further, the pins are flattened in the portion which engages the locking surface to distribute the load over a broad area of the locking surface. Also, the outer ends of the pins are cylindrically shaped, where the radius of the cylindrically shaped ends matches the inside radius of the annular groove that is formed in the inner wall of the outer section.
A deactivation hydraulic valve lifter in accordance with Church et al. can be vulnerable to reliability problems. First, the sharp 90xc2x0 inner corner of groove 69, as shown in FIGS. 3 and 4, focuses stress on the latching surface in the groove and can lead to stress failure of the outer body member 17 at that point, particularly when, during erratic pin engagement, a single pin carries the majority of the load for one or more engine revolutions. Further, the entrance edge or corner of latching surface 71 is vulnerable to damage or distress by the lower corner of latching member 63 during repeated latching and unlatching as the member corner is released by the entrance corner of the latching surface, which distress can cause the latching member (locking pin) either to jam in the locked position or to refuse to engage into the locked position. Also, the metal around the circumferential edge of the transverse bore is vulnerable to stress or distortion from repeated loading of the locking pins. Such metal distortion can impart shearing forces across the entrance edge of the annular groove when the pin housing slides within the axial bore of the lifter body.
In addition, the Church et al. patent fails to disclose a means for adjusting mechanical lash in the deactivation mechanism caused from inherent manufacturing variability in the deactivation components. The entire assembly is held together by a standard stop clip 39 which is full-fitting in a groove in outer body member 17, as shown in FIG. 3. Thus, the amount of lash between latching member 63 and latching surface 71 after assembly cannot be compensated or adjusted in individual lifter assemblies.
It is a principal object of the present invention to provide an improved valve-deactivation hydraulic lifter wherein reliability is increased by reconfiguring locking components to reduce distress and thereby reduce sticking susceptibility between the locking pins and the locking groove.
It is a further object of the invention to provide such a lifter wherein mechanical lash in the deactivation mechanism can be readily adjusted during assembly of the lifter.
Briefly described, a valve-deactivation valve lifter in accordance with the invention includes a pin housing that is slidably disposed within an axial bore in a lifter body. A transverse bore in the pin housing contains two opposed locking pins urged outwards of the pin housing by a pin spring disposed in compression therebetween to engage a circumferential groove including a locking surface in the lifter body whereby the lifter body and the pin housing are locked together for mutual actuation by rotary motion of the cam lobe to produce reciprocal motion of an engine pushrod. The pins may be disengaged from the lifter body by application of hydraulic fluid such as engine oil through one or more fluid ports to the outer ends of the pins at pressure sufficient to over come the force of the pin spring.
The outer most ends of the locking pins are generally spherical and their leading edges chamfered such that the pins cannot block nor enter the fluid ports and the leading edges cannot contact a conjunctive corner within the circumferential groove wherein the radial wall of the groove meets the axial locking surface of the groove. Further, the entrance edge of the locking surface is also chamfered to prevent mutual abuse and distress at the leading edge of the pin and entrance edge of the groove during locking and unlocking, which distress is known to cause sticking of pins in prior art lifters. In addition, the conjunctive corner of the groove is rounded by a radius such that a sharp corner is obviated, which sharp corner is known to be an originating and propagating point for stress failure of the lifter body in prior art lifters. A relief is also provided on the pin housing circumscribing the ends of the transverse pin bore to reduce metal distress around the outside edges of the bore and to prevent any deformation of the pin housing""s cylindrical surface at the edges of the bore from shearing across the entrance edge of the circumferential groove in the lifter body. Further, the snap ring holding the lifter assembly together also functions to set the mechanical lash in the deactivation mechanism. The latch adjusting feature may be provided as a one-part ring of a selected thickness or as a two-part ring, the first part being a standard-thickness ring and the second part being a shim whose thickness is selected to provide a predetermined amount of lash therein.